Radio apparatus



Jlme 13, 1933 H. M., THRELKELD 1,913,461

RADIO AFPARATUS Filed Sept. 14, 1931 2.ShetS-Sheet 1 .EMPL/HEL? P IC frP K 6' l?. E Po WEP DErEcfo/a E Hol/wp men/(n.0.

' ATTORNEY.

June 13' V1933- H. MQ THRELKELD 1913,461

RADIO APPARATUS Filed Sept. 14, 1931 2 vSheets-Sheet 2 Powie i 5 Sz/PPLY:lr 4

I N VEN TOR.

EEZ/(EAD A TTORNEY.

Patented .lune 13, 1933 y, UNITED STATES PATENT OFFICE rIowAnn 1v1.rneniinnnn, on noLLYWoon, onnrronnrm AssIGNon To GRIGSBY- e-nUNoWconn/inner cHIoAGo, ILLINOIS, A CORPORATION oFIIiLINoIs RADIO APPARATUSf Application mea september 14, 19:31.` serial No. 562,661.`

This invention relatesto radio apparatus, and particularly to theautomatiecontrol of volmne. yIn systems wherein a separate tube is used`to automatically maintain a constant volume of reproduction,` it hasbeen found `that there is an appreciable variation of volume withrespect to signal strength; `This is primarily due to the fact that thepower supply potential applied to the automatic volume control tubechanges, due to the poor regulation of the customary power supplies.Thus, it is usual to impress rectified and filtcred current on avoltagedivider', usually a series of resistances, and appiy the variouspotentials along" these resistances to thevarions portions ofctheset, asneeded. Ob-` viously, the variati ouin plate current through the R.F.tubes due to variation of signal strength, results in variation ofpotential along various portions of the voltage divider. V Anfobjectofthis invention is to devise a system in which the volume will maintainedconstant over a wide range of signal strength. i 1 r An additionalobject is to devise` a system in which the,characteristic,of the volumecontroi may be very simply and easily pjedet'ei|- mined.` ,y

In general, this, invention `contemplates the selection` of two points`on `the voltage divider having opposite voltage vcharacteristics. Thus,npona decrease in load of the R. F. ampliliers, one point may have arising voltage characteristic, while the other point may have a falling`voltage characteristic. These two points are suitably bridged in suchmanner that a, neutral point having a substan tially consu-.int "voltageAchaiacteristic is created.` This neutral point, or as later cir-Vplained a pointad'jacent thereto, is suitably connectedto the` cathodeofthe automatic volume control tubehereinafter al idged to CIIpotential" oflthesystem.` This permits the potential of theother jelectrodes to vary in accordance with the laws governing the va-` riousportions of the system and permits these other electrodes `to morefaithfully perform their automatic volume control functions.` i p y Thissystem is particularly effective when used in connection with a detectorin which the variation of grid potential during detection has a widerange, suclias` in socalled power detectors.

In the drawings,

Figurel a diagrammatic,showing of a receiver having a three-element A.V. C. tube connected in accordance withfthis invention;

Figure2 issimilar to Figure l with the exception that afour-element A.V. C. tube is disclosed;` and i o,

` Figure 3 shows the application of this invention to a superheterodynetype of circuit.

" Referring to Figure 1, an antenna and ground are shown connected to anR. F. amplier.l This amplifier `may beof any type lwhatsoever, havinganynumber of stages and using any suitable types of tubes. For

as having three connections, P, Kand G,

' being the plate, cathode and grid connections,

respectively.` It is understood, of course, that "the stages may beeliminated. The R. F.

amplifier leads into a power detector having three similar connectionsand finally energizes suitable audio-frequency amplifiers and apparatus(not shown) In order to energize the set, a power supply ofthe usualtype, having a. rectifier `and suitableflters andchokes, may be providedand connected to a source of alternating current. `The positivepotential ofthe power Vthe, salreof simplicity, this amplifier is shownf supply is connected to terminal 1 of the voltage divider 2, 1 usuallyconsisting of one or more resistances, The other terminal 3 of voltagedivider 2 is grounded and connects with the grounded negative terminalof the power supply. Thus, during the operation of the power supplythere will be current fiowing through the voltage divider all the time.Terminal P of the R. F. amplifier is connected through a tuning meter 5to terminal 1 of voltage divider 2. Cathode K of R. F. amplifier isconnected through a suitable resistance 6 and lead 7 to point 8 onvoltage divider 2. Points 8 and 1 are so chosen with respect to eachother that the difference in potential thereof is suitable :forenergizing the plate circuits of the R. amplifier. In order to obtainthe grid bias in the R. F. amplifier, grid terminal G is connected tolead 7 through a resistance 10, whose function will be explained later.Due to the drop in potential along resistance 6, Cathode terminal K willbe at a positive potential with respect to lead 7. Grid terminal Gr,which 1s connected to lead 7 through resistance 10 of a suitable value,will, therefore, be maintained negative with respect to cathode K.

The power detector plate terminal P is similarly connected to terminal 1of the voltage divider 2, through a resistance 11. This resistance isinserted merely to adjust the potential of P to the proper value.Obviously, this same effect may be obtained by connecting the plateterminal of the power detector to a suitable point along voltage divider2. lathode K of the power detector is grounded through resistance 12.Grid Gr of the power detector is connected through a lead 13 to thegrounded end of resistance 12. The grid bias in the power detector will,therefore, be maintained in substantially the same manner as in the R.F. amplifier. The actual values of the various potentials may beadjustedby suitably adjusting the values of the various resistances. l Y

The three-elementA. V. C. tube has its plate and grid connected intheusualv manner. The plate 15 is connected through lead 16 to the 'gridterminal of the R. F. amplifier. A variable condenser 17 is connectedbetween lead 16 and ground. Grid 20 is connected through a resistance 21to the cathode ofthe power detector.

In order to provide aV connection through cathode 23 of the A. V. C.tube, two points, 1 and 8, on the voltage divider 2 are connectedthrough a resistance 25. It is not necessary that resistance 25 beconnected to the same points on voltage divider 2 as the anode andcathode of the R. F. amplifier. It is only necessary to use two pointsalong voltage divider 2 which have opposite voltage characteristics witha change of load through the R. F. amplifiers. For simplicity ofconnections, points 1 and 8 are taken. Along a suitable point 26, whichmay be eXperid mentally determined, one end of resistance 27 isconnected. As explained later, point 26 is close to neutral point N, thelatter having a constant potential for variations of load. The other endof resistance 27 is connected to a point 28 on voltage divider 2.Resistance 27 is provided with a sliding contact 30, thus making it apotentiometer. Slider 30 is connected through a lead 31 to cathode 23 ofthe A. V. C. tube.

It is understood, of course, that the various points along voltagedivider 2, as well as the values of the various resistances, are l sochosen that the various electrodes of all power detector, there will bean increase in T the drop through resistance 12, with the result thatthe cathode K of the detector will tend to become more positive. Thiswill result in the potential of grid 2 becoming more positive andpermitting greater space current to flow through the A. V. C. tube.

Assuming the conventional fiow of current from positive to negativeterminals of the system, it is clear that the A. V. C. tube will drawmore current through resistance 10. The drop along this resistance will,therefore, become greater, with the result that grid terminal G of theR. F. amplifier will tend to become more negative with respect tothecathode of the R. F. amplifier. will, therefore, cut down the platecurrent through the R. F. amplifier to normal value. The time constantof the plate circuit of the A. V. C. tube may be adjusted by usingproper values for the resistance 10 and condenser 17.

As the load through the R. F. amplifier tends to increase, due to anincrease in volume, more current is by-passed through the R. F.amplifier tubes and less through voltage divider 2. This results in thepotential of point 1 dropping somewhat and the potential of point 8rising somewhat with respect to normal values. sistance 25, which isalmost at a constant potential with respect to ground, will thus tend tomaintain cathode 23 of the A. V. C. tubes at a substantially constantvalue, taking into account the poor regulation of lower portion ofresistance 27 and the por- During the normal operaif f LLI/O This I i'Point 26 on rei tion ofthedivider'below point As the space `currentthrough the A. V. C. tube tends to vary, the drops through portion 35`and the portion of voltage divider 2be1ow point 28 varies. Hence, bymoving point 26 a little away from the theoretical neutral point,indicated at N, the potential applied to resistance 27 will tend to dropsomewhat i as the R. F; amplifier ytends to pass more currenttherethrough.` 2 i This point26, however, may vary on one side or theother 'of the neutral point and may `be experimentally determined. Infactybyvarying the` position of point 26 with respect to the trueneutral point N, the

characteristic curve `of the volume control systemmaybe caused to slopeupwardly or dip downwardly, `thus giving.-` somewhat greater volume` inlthe first case and somewhat less lvolumexin the second case for an iincrease inf signal strength.`

c In orderV to1perm1taccurate tuning of the set, the usual tuning meter5'is` disposed vin current through the A. V. C. tube in the event thatthe potential of grid will swlng positive with respect to cathode 23 ofthe A. V. C.l

tube. This, of course, is possible with a sufficiently large surge`through thepower detector. i Y i i. y t@ The` actual volume of thesetmay bevariedby moving slider along resistance 27. i In Figure` 2, the A.V: C. tube` is provided `with a shield gridu40. This `additional grid isconnected by a lead 41 `to point 42 on voltage divi-der 2. Point12soichosen that a suitable potential is imposed on the` shield grid.`1n order to compensate for the regulation of` potential at point 42 ofthe volt-` divider, resistance27 will have to `be i connectedat adifferentpoint 26 .o`n resistance 25. Inf this instance, some additionalpoor regulation is introduced in the cathode `circuit of the A. VJC;tube to compensate forthe inherently poor regulation of hetercdyne, in asimple form, comprises an antenna tuning condenser 60, having oneterminal grounded and theother terminal connectedto an inductance 611Inductancel61 is connected to grid 62 and through a.blockingcondenser63,to cathode 54 of the radio `frequency amplifier. The anode65 of the R. F. tube isv connected through the primary of thetransformer 66 to a lead 67 The low side of inductanee 61 is connectedto a lead 68. Cathode 64 is` grounded,` as faras radio-` frequency`impulses are concerned, through a condenser 69. The :secondary oftransormer66 has one terminal connected to lead 68, while its otherterminal isconnected to grid 72 of detector tube D. A tuning condenser73 is connected between grid 72 and ground. Cathode 74 is connectedthrough a pick-up coil 75 and biasing resistance 76, to a lead 77Pick-up coil 7 5 isinductively associated with` coils 78 and 79 in thegrid 'and `plate circuits, respectively, of the os- Grid 80of theoscillator tube i cillator tube. is connected to coil 78 by leadl 81,and a blocking condenser 82 isinserted in return lead 83 to the cathode.Ar grid resistance 811 and timing condenser 85, are connected acrossfrom grid 80 to cathode 86 of the oscillator tube. Plate 87 of theoscillatortube is connected through coil 79 to lead 88. Anode 89 of thefirst detector tube is connected through the primary of the intermediatefrequency transformer 90 to alead 91, which isconnected to lead 67. Theprimary transformer 90 has its lowerend connected to a groundedcondenser 92. The secondary of transformer 90 is connected between lead68 and grid 93 of the intermediate frequency amplifier. A tuningcondenser 94 is connected between grid 93 and ground. Gathode 95isconnected to lead 77, which connects cathodes 64, 74 and 95, andleadstoa tuning meter 96. The other terminal of me-` ter 96 is connectedthrough a bias resistance 97 to lead 268. Anode 98 of the intermediatefrequency amplifier is connected through the primary of a transformer 99to anode post 91 and thence to ground through a condenser 100. Thesecondaryoftransformer199 is connected to` grid 101 of a second detectorand also to ground. A tuning condenser 102 is shunted across" thesecondary. Cathode 103 `is grounded to a biasing resistance 104i. Anode105 of the seconddetector is connected to the primary of `anaudio-frequency transformer 106 toanode post 91 andto grounded condenser107. The secondary of transformer 106 feeds audio-frequency to asuitable amplifier and translating means (not shown.)

Apower supply of the usual type has its positive pole connected toterminal 201 of thevoltage divider 202. Lead 67, supplying variousanodes, is connected to the voltage divideratthis point. The otherend ofthe voltage divider is grounded.` Lead 68, supplying potential tothegrids of various tubes is connected through a resistance 269 to lead268. Lead 268 is brought to point 208 on the voltage divider. Lead 88,connecting through the plate 87 of the oscillator tube, taps on point250 of voltage divider 202. The

various shield grids 251 ofthe radio-fre-` quency and intermediatefrequency amplifiers and first detectors are connected through vlead 252-to a suitable point Y253 on divider 202. Shield grid 255 is connectedthrough a lead 256 to point 257 on divider 202.

Anode 270 of the A. V. C. tube is connected by lead 271 to lead 68supplying potential to the R. F. grids. Grid 272 of this tube isconnected through a regulating resistance 273 to thev cathode 103 ofthey second detector. Shield grid 274 is given a suitable potential byconnecting it to a point 275 on the voltage divider. Cathode 276 of theA. V. C. tube is connected through a lead 277 to a slider 278 operatingon resistance 280. This latter resistance is connected from ground to asuitable. point 281 on bridge resistance 282 connected between points201 and 208 on the voltage divider. i

Inasmuch as the operation of this circuit is Similar to that shown inFigure 2, no detailed explanation is necessary.

I claim 1. In a radio system of the type having a radio frequencyamplifier, a power supply including' a voltage divider with a poorregulation characteristic, and provided with a detector adapted tofunction over a substantial input voltage range, the combination of anautomatic volume control circuit comprising a vacuum tube, connectionsfrom said power supply to said tube for energizing the latter, saidconnections including a resistance in the radio frequency grid circuitand a connection from the anode of said automatic volume control tube tothe low side of said resistance, a connection from the grid of saidautomatic volume control tube to the cathode of said detector, a bridgeresistance connecting two points on said voltager dividerV havingopposite voltage regulation characteristics, an additional resistanceconnected between a point on said voltage divider and a point on saidbridge resistance, said bridge resistance point being at a higherpotential than said voltage divider point, and a connection from thecathode of said automatic volume control tube to a point on saidadditional resistance.

2. In aradio receiver of the type having a radio frequency amplifier, apower detector and a power supply including a voltage divider having apoor regulation characteristic and having a separate automatic volumecontrol tube with circuit connections, whereby the grid bias ofthe radiofrequency amplilier is a function of the space current through theautomatic volume control tube, the combination of means for obtaining apredetermined automatic volume control characteristic comprising abridge Vresistance connecting two points on said voltage divider havingopposite load potential characteristics, whereby a. neutral point onsaid bridge resistance exists where the potential is substantiallyconstant with varying load during the normal operation of the set, asecond resistance connected to a point on said bridge resistance intheneighborhood of the neutral point, the other .end of said secondresistance being connected to the voltage divider at a point near thelow potential end thereof, and adjust-able means for connecting thecathode of said automatic volume control tube to a predetermined portionof said second resistance.

3. In a radio receiver of the type having a radio frequency amplifier, apower detector and a power supply including a voltage divider having apoor regulation characteristic and having a separate automatic volumecontrol tube with circuit connections whereby the grid bias of the radiofrequency amplifier is :a function of the space current through theautomatic volume control tube, the combination of a bridge resistanceconnected' between two points on said voltage divider having oppositevoltage characteristics so that said bridge resistance has a neutralpoint thereon of substantially constant potential during normal loadvariations and connections from the cathode of the automatic volumecontrol tube to said bridge resistance at a point in sufficientproximity to said neutral point to compensate for the regulationcharacteristic of the resistance in the automatic volume control cathodecircuit and thus obtain a predetermined automatic volume controlcharacteristic.

t. In a radio vreceiver of the type having a radio frequency amplifier,a power detector and a. power supply including a voltage divider havinga poor regulation characteristic and having Ia separate automatic volumecontrol tube of the shield grid type, said tube having circuitconnections whereby the grid bias of the radio frequency amplifier is afunction of the space current through the automatic volume control tube,the combination of means for obtaining a predetermined automatic volumecontrol characteristic comprising a bridge resistance connecting twopoints having opposite voltage characteristics on said divider whereby aneutral point on said bridge resistance is formed,va second resistancehaving one end connected to .a point on said divider in proximity to itslow potential end, means for connecting said automatic volume controlcathode to a predetermined point onsaid second resistance, and means forconnecting the other end' of said second resistance to a point on saidbridge resistance, said last point being so related to said neutralpoint that a predetermined degree of voltage regulation is introduced tocompensate for the inherently poor regulation of the resistance in theautomatic volume control cathode circuit and also in the shield gridcircuit. Y

In testimony whereof he affixes his signature.

HOWARD M. TI-IRELKELD.

